Pulse oximetry is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood. FIG. 1 illustrates a pulse oximetry system 100 having a sensor 200 attachable to a patient 10, a host instrument 310 for monitoring oxygen saturation and pulse rate, and a patient cable 350 that connects the sensor 200 and the host instrument 310. The sensor 200, can be attached to an adult patient's finger or an infant patient's foot, for example.
FIG. 2 illustrates a sensor 200 having both red and infrared LEDs 210 and a photodiode detector 220. The sensor 200 is configured so that the LEDs 210 project light through the blood vessels and capillaries of a tissue site. The photodiode 220 is positioned at the tissue site opposite the LEDs 210 so as to detect the LED emitted light as it emerges from the tissue site. The sensor 200 has LED pinouts 240 and photodiode pinouts 250 that provide a connection to the host instrument 310 (FIG. 1) via the patient cable 350 (FIG. 1). A pulse oximetry sensor is described in U.S. Pat. No. 6,256,523 entitled “Low-Noise Optical Probes,” assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein.
As shown in FIG. 2, the sensor 200 may also have a identification (ID) element 230. The ID element 230 may be any circuit element, such as a resistor having a predetermined value, that provides information regarding the sensor 200. This information may be used, for example, to indicate the sensor manufacturer or supplier. The ID element 230 may be located in parallel with the LEDs 210 so as to share the LED pinouts 240. The host instrument 310 (FIG. 1) may be programmed to operate only if it is connected to a sensor 200 that it recognizes is from an authorized source. This feature maintains sensor and measurement quality control and ensures patient safety. Sensor identification and information elements and are described in U.S. Pat. No. 6,011,986 entitled “Manual And Automatic Probe Calibration,” which is assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein.
FIG. 3 functionally illustrates a pulse oximetry system 100 having a sensor 200, a host instrument 310 and a patient cable 350. The host instrument 310 has LED drivers 312 that alternately activate the sensor red and IR LEDs 210. A signal conditioner 315 processes the resulting current generated by the photodiode detector 220, which is proportional to the intensity of the detected light. A signal processor 316 inputs the conditioned detector signal and determines oxygen saturation based on the differential absorption by arterial blood of the two wavelengths emitted by the LEDs 210. Specifically, a ratio of detected red and infrared intensities is calculated by the signal processor 316, and an arterial oxygen saturation value is empirically determined based on the ratio obtained. Computed oxygen saturation and pulse rate are provided on the host instrument display 318. An ID reader 314 is capable of determining the ID element 230. A host instrument signal processor is described in U.S. Pat. No. 6,081,735 entitled “Signal Processing Apparatus,” which is assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein. A patient cable 350 has shared LED drive/ ID lines 352 that provide communications between the host instrument LED drivers 312 and ID reader 314 and the sensor LEDs 210 and ID element 230 via shared LED pinouts 240 (FIG. 2). Photodiode lines 354 provide communications between the sensor detector 220 and the host instrument signal conditioner 315.